Spawning time of two shallow-water brittle stars

Abstract

Broadcast spawning, wherein gametes of both sexes are released for external fertilization, is a common mode of reproduction in marine organisms. Despite its importance in the life histories of many species, discovery of its timing is often based on chance observations. Here we report on the spawning of 2 shallow-water brittle stars in southern Taiwan known to have spawning induction, i.e. ovary homogenates induce spawning of conspecific males. The gonad index of both species exhibited an annual cycle with peaks from mid-spring to early summer. Successful induction of spawning in male Ophiocoma scolopendrina (Lamarck) inhabiting the intertidal zone was limited to low tides. After manipulating the depth of the water inhabited by brittle stars, we discovered that successful induction of spawning was not sensitive to the actual water level. However, males could consistently be induced to spawn at the time of low tides even when deprived of tidal influences in the laboratory. Therefore, an endogenous clock mechanism entrained by tide-associated phenomena may control the inductivity of mature male O. scolopendrina. Time of the day, i.e. day versus night, had no effect in this species. In O. dentata (Müller and Troschel) living in the shallow subtidal zone in the same area, male induction was successful during both high and low tides and in both day and night. © Inter-Research 2009.